1. Field of the Invention
This invention relates to a recording apparatus for performing transfer recording with a laser beam from an optical head being applied to a recording medium fixed on a recording rotating drum, more particularly, to one that is free from the problem of density drop.
2. Description of the Related Art
The recording apparatus contemplated by the invention records image with a laser beam from an optical head being applied to a recording medium fixed on a recording rotating drum (hereunder referred to as a xe2x80x9crecording drumxe2x80x9d) or a recording plane. The recording medium is the collective term for the combination of an receiver film fixed on the rotating drum and a transfer film fixed onto the receiver film to cover it.
FIG. 8 shows in conceptual form the entire part of the recording apparatus contemplated by the invention. The recording apparatus generally indicated by 30 is adapted for producing a full color image and to this end, it comprises a recording medium supply section 32, a rotating drum 34, a recording medium fix/release mechanism 36 provided on the rotating drum 34, a laminating mechanism 38 provided along the periphery of the rotating drum 34, an optical head 40, a stripping mechanism 42, a sheet feed section 44, a laminating section 46, a fixing section 48, a stripping section 50, a tray section 52 and a control section 54.
In the recording apparatus 30, the recording medium supply section 32 supplies an receiver film R and a transfer film T onto the rotating drum 34. The receiver film R is first fixed on the rotating drum 34 by means of the recording medium fix/release mechanism 36 and then the transfer film T is superposed on the receiver film R as it is adhered under thermal compression by the laminating mechanism 38. The heating step may be omitted depending on the type of the recording medium used.
In the next step, the optical head 40 being controlled in accordance with a picture signal by the control section 54 performs imagewise exposure with a laser operating in heated mode to record a latent image. Subsequently, the transfer film T is stripped from the receiver film R remaining on the rotating drum 34 by means of the stripping mechanism 42, whereupon the latent image on the transfer film T is transferred to the receiver film R and developed to form a visible image on the receiver film R. The same procedure is repeated for 3 or 4 colors to form a color image on the receiver film R which, in turn, is laminated with hard sheet H supplied from the sheet feed section 44. After adhesion, an image receiving layer 16 in the receiver film R is photocured in the fixing section 48. The hard sheet H now having the full color image is stripped from the receiver film R in the stripping section 50 and ejected onto a proof tray 52a whereas the receiver film R is ejected into a waste stacker 52b. 
In this way the full color image is obtained as a hard copy. The recording medium supply section 32 comprises a recording medium station 53 holding a plurality of recording mediums (i.e., rolls of heat sensitive materials such as a roll of receiver film R and a plurality of transfer films T such as standard transfer films for K (black), C (cyan), M (magenta) and Y (yellow) as well as sheets for special colors like gold and silver that are used in the printing field), a pair of rollers 54 for pulling out a single recording medium, a cutter 55 with which a predetermined length of the recording medium pulled out of the recording medium station 53 by the pull-out rollers 54 is cut in sheet form, a pair of rollers 56 for nipping and transporting the sheet of recording medium, and a guide 57 with which the sheet of recording medium is guided on the rotating drum 34 up to the position where the leading edge of the recording medium is fixed by the recording medium fix/release mechanism 36 on the rotating drum 34.
The receiver film R is first supplied to the rotating drum 34. Its leading edge is clamped or otherwise fixed to the mechanism 36 and, as the rotating drum 34 rotates in the direction of the arrow, the receiver film R is wound onto the outer surface of the rotating drum 34. The trailing edge of the receiver film R is also fixed by the recording medium fix/release mechanism 36. Preferably, at least one of the portions of the recording medium fix/release mechanism 36 which fix the leading and trailing edges of the receiver film R is adapted to be movable on the outer surface of the rotating drum 34 so that various lengths of recording medium in sheet form can be fixed onto the rotating drum 34.
After the receiver film R has been wound onto the periphery of the rotating drum 34, the transfer film T that has been transformed from the recording medium supply section 32 in a completely identical manner is wound onto the receiver film R in superposition. This step of superposing the transfer film T on the receiver film R is performed by the laminating mechanism 38 consisting of a laminating roller 58 having a built-in heater (not shown), an arm 59 which rotates the laminating roller 58 about a fulcrum 59a so that it contacts or separates from the outer surface of the rotating drum 34, and a depressing means 60 for depressing the laminating roller 58 against the outer surface of the rotating drum at a predetermined pressure. The depressing means 60 may be an urging means such as a spring or an air cylinder manipulator.
The image receiving layer forming the outermost part of the receiver film R is tacky and can be laminated with the transfer film as it is depressed under a predetermined pressure by the laminating roller 58. Therefore, the image receiving layer in the receiver film R and the toner layer in the transfer film T can be adhered to each other not only without developing wrinkles and other surface defects in the transfer film T but also achieving a uniform adhesive force.
In order to ensure uniform and strong bonding, the transfer film T is laminated to the receiver film R by means of the pressure laminating roller 58. In order to provide a greater adhesive force, the laminating roller 58 is preferably heated as it is pressed onto the rotating drum during lamination. The heating temperature is not more than 130xc2x0 C., preferably not more than 100xc2x0 C.
When winding the receiver film R onto the rotating drum 34, its leading edge is preferably fixed by the recording medium fix/release mechanism 36 while the other portion is retained by the transport roller pair 56 or the laminating roller 58 or some other means so that it can be wound onto the periphery of the rotating drum 34 under tension. As will be mentioned later, suction holes may be formed in the outer surface of the rotating drum 34 so that the receiver film R can be sucked onto the rotating drum by a suction means. While the suction means is preferably used in combination with the recording medium fix/release mechanism 36, either one of them may be used alone. In this way, the receiver film R can be fixed onto the periphery of the rotating drum 34 without developing wrinkles or other surface defects and without causing positional offsets. Tension is preferably applied when the transfer film T is superposed on the receiver film R after it has been wound onto the rotating drum 34. Again, the recording medium fix/release mechanism 36 may be used to fix the leading edge and/or trailing edge of the transfer film T and the above-mentioned suction means may also be used in combination with the recording medium fix/release mechanism 36. Preferably, the tension to be applied to the transfer film T being superposed is smaller than the tension to be applied to the receiver film R as it is wound onto the rotating drum 34.
The optical head 40 comprises a laser head 24 and an sub scanning means 61. The laser head 24 consists basically of a laser beam source which includes a modulation means and emits high-density energy light such as a laser beam and an imaging lens which adjusts the diameter of a beam spot of laser beam. The sub scanning means 61 moves the laser head 24 axially or in a direction parallel to the shaft of the rotating drum 34 (normal to the paper of FIG. 8) for performing sub scanning.
To perform main scanning of the transfer film T with laser beam, the rotating drum 34 is rotated. If desired, the sub scanning means 61 in the optical head 40 may be replaced by an axial moving means on the rotating drum 34 so that the latter is rotated for main scan and moved axially for sub scan.
Any laser beam source will do as long as it can emit high-density energy light capable of exposure in heated mode and exemplary lasers that can be used include gas lasers such as an argon ion laser, a helium neon laser and a helium cadmium laser, solid lasers such as a YAG laser, semiconductor lasers, as well as dye lasers and excimer lasers. Modulation of laser beam with a picture signal can be performed by any known methods; in the case of an argon ion laser, the laser beam is passed through an external modulator; in the case of a semiconductor laser, the electric current being injected into the laser is controlled by a signal (to effect direct modulation). The size of the laser spot formed by focusing on the opto-thermal converting layer and the scanning speed are set in accordance with the resolving power required for the image to be recorded and the recording sensitivity of the material. For use in printing, high resolving power is generally required and better image quality is obtained by a smaller beam spot; on the other hand, the depth of focus is so small that it is difficult to control mechanically. If the scanning speed is unduly slow, the heat loss due to heat conduction to the support of the transfer film so much increases that energy efficiency decreases and the recording time increases. In view of these, the recording conditions to be adopted in the present invention are such that the beam diameter on the opto-thermal converting layer is 5-50 xcexcm, preferably 6-30 xcexcm, and the scanning speed is at least 1 m/s, preferably at least 3 m/s.
The picture signal as sent to the recording apparatus 30 of the invention from an external image reading apparatus, image processing apparatus, work station (W/S) having a DTP capability, electronic publishing system and various storage media (e.g., magnetic tape, floppy disk, hard disk and RAM card) is transmitted to the control section 54 as a digital signal via an interface or the like, given necessary processing and further transmitted to the optical head 40 for controlling exposure to the laser in heated mode on the laser head 24.
The control section 54 controls not only sub scan by the sub scanning means 61 on the optical head 40 and main scan by the rotation of the rotating drum 34 but also the operation of the individual parts of the recording apparatus 30 and the overall sequence of their operations.
The first function of the stripping mechanism 42 is to strip the transfer film T from the receiver film R after a latent image has been formed on the transfer film T by exposure to the laser in heated mode on the optical head 40. The second function of the stripping mechanism 42 is to help transfer the latent image onto the receiver film R for subsequent development. To perform these functions, the stripping mechanism 42 comprises a strip roller 62, two split rollers 63 and 64 in contact with the strip roller 62, a comb-toothed guide plate 65 provided between the segments of each split roller (63, 64) along the strip roller 62, and a bracket (not shown) on which these components are mounted integrally. The strip roller 62 is axially supported on an arm 67 and rotates about a fulcrum 67a so that it contacts or separates from the outer surface of the rotating drum 34. Also provided is a depressing means 68 by which the strip roller 62 is pressed against the laminate of the receiver film R and the transfer film T on the rotating drum 34 via the arm 67.
When the laminate of the transfer film T having a latent image formed on it as a result of decrease in the adhesion of the toner layer 22 due to imagewise application of thermal energy upon exposure to the laser in heated more and the receiver film R having the image receiving layer 16 adhered to the toner layer 22 has come close to the stripping mechanism 42, the arm 67 rotates about the fulcrum 67a to bring the bracket closer to the laminate and the comb-toothed guide plate 65 is slipped between the image receiving layer 16 in the receiver film R and the toner layer 22 in the transfer film T while, at the same time, the laminate is depressed from the transfer film (T) side by the strip roller 62. If the transfer film T and the receiver film R to be joined are slightly offset in length, the comb-toothed guide plate 65 can be easily slipped between the two sheets. After the above-described step, the rotating drum 34 is rotated and, at the same time, the strip roller 62 and the split rollers 63 and 64 are rotated so that the leading edge of the transfer film T is moved along the comb-toothed guide plate 65 until it is nipped between the strip roller 62 and each of the split rollers 63 and 64. Thus, the transfer film T as it is depressed by the strip roller 62 is nipped between the strip roller 62 and each of the split rollers 63 and 64 and transported so that it is stripped from the receiver film R. Since the transfer film T is stripped from the receiver film R at a constant speed in the area depressed with the stripping roller 62, the stripping force can be held constant and, in the absence of any vibrational phenomena such as stick slip, there will be no unevenness in stripping. Since the stripping force being applied to the receiver film R does not vary during stripping, there will be no offset in the position where the receiver film R is fixed on the rotating drum 34. This eliminates the possibility of drop in the precision of registration. Hence, one can produce a monochromatic halftone image of high quality, high resolution and high gradation that is free from unevenness in stripping, misregistration and any other defects.
By repeating the same procedure for C, M, Y and K colors, four color images are stripped, transferred and developed in exact registration on the receiver film R, which is then guided by two guides 70 for transport to the laminating section 46 by means of a transport roller 71.
In the laminating section 46, a hard sheet supply roll 72 delivers a hard sheet H from a cassette 73 in synchronism with the transport of the receiver film R and the hard sheet H is transported to the right of FIG. 8 as it is guided by the guide member 70. If desired, the hard sheet H may be fed to the hard sheet supply roller 72 along a hand-feed chute 44a. Subsequently, the receiver film R and the hard sheet H are laminated with registry achieved by a registration roller pair 75 and the resulting laminate is transported to the fixing section 48.
The laminating section may be provided as a separate entity from the recording apparatus.
In the fixing section 48, the laminate of the receiver film R and the hard sheet H is nipped and transported by a heat/fix roller pair 76 consisting of a compression roller 76aand a heating roller 76b so that it is heated for fixing. The laminate is also subjected to post-exposure under uv lamps 77 so that the image receiving layer 16 in the receiver film R hardens to become readily strippable.
This fixing step may be omitted depending upon the type of the recording medium used.
In the next step, the laminate goes to the stripping section 50, where the readily strippable image receiving layer 16 is stripped from the other part of the receiver film R by means of a stripping roller pair 78 and a stripping guide 79, whereupon the image receiving layer 16 adheres to the hard sheet H to have the image transferred to the latter. The hard sheet H now carrying the transferred image is ejected as a hard copy onto the proof tray 52a in the tray section 52 whereas the receiver film R which has been stripped of the image receiving layer 16 is dumped into the waste tray 52b. 
FIG. 9 is a perspective view showing the essential parts of the recording apparatus shown in FIG. 8. Referring to FIG. 9, numeral 1 designates the optical head capable of one-dimensional movement and which emits a plurality of laser beams that can be modulated to turn on and off in accordance with the data to be recorded; 2 is the fast rotating drum with a recording medium mounted thereon; 3 is the recording medium having a different structure depending upon to which use it is put, such as for use in CTP (computer to plate), DDCP (direct digital color proofer) or lithography; 4 is a moving stage (or an sub scanning stage) which, with the optical head 1 mounted thereon, is capable of moving along rails in a direction parallel to the recording medium 3 on the rotating drum 2. As the stage 4 moves, the optical head 1 applies a laser beam to the recording medium 3 for recording purposes. The movement of the stage 4 corresponds to sub scan in image formation and main scan is performed in the rotating direction of the drum 2.
We now describe the structure of the recording medium 3 with reference to FIG. 10 which shows separately the receiver film R and the transfer film T that combine to form the recording medium 3 shown in FIG. 9. In the actual step of recording on the recording medium 3, a thermal transfer sheet is used that constitutes a recording medium of the type shown in FIG. 10. The transfer film T consists of, in order from the side to be illuminated with laser beam, a support, an opto-thermal converting layer and a toner layer whereas the receiver film R consists of, in order from the transfer film (T) side, an image receiving layer, a cushion layer and a support. The transfer film T is superposed on the receiver film R, with the toner layer in contact with the image receiving layer, and the resulting laminate is illuminated with laser beam, whereupon the illuminated part of the toner layer is thermally transferred to the image receiving layer.
The support in the transfer film T shown in FIG. 10 is made of a laser beam transparent material such as a PET (polyethylene terephthlate) base, a TAC (triacetyl cellulose) base or a PEN (polyethylene naphthalate) base. The opto-electric converting layer is made of a material capable of efficient conversion of laser energy into heat and examples of such material include carbon, a black substance, an infrared absorbing dye and a specified wavelength absorber. The toner layer is available as transfer films of K (black), C (cyan), M (magenta) and Y (yellow) colors. Transfer films of various other colors such as gold, silver, brown, gray, green and orange may sometimes be used. Transfer films of different colors have different heating and recording characteristics.
The image receiving layer in the receiver film R serves to receive the toner being transferred from the transfer film T. The cushion layer is capable of absorbing the steps that may form when more than one stack of toner is provided.
The structures described above are variable with specific use and details about the toner and receiver films to be used are given in commonly assigned Unexamined Published Japanese Patent Application (kokai) Nos. 296594/1992, 327982/1992 and 327983/1992. An apparatus using such recording materials is also disclosed in commonly assigned Unexamined Published Japanese Patent Application (kokai) No. 290731/1995.
FIG. 11 shows the sequence of steps in the process of recording K, C, M and Y images on the receiver film R shown in FIG. 10. The process of recording each monochromatic image generally consists of three steps, laminating, laser recording with color data, and stripping the transfer film T from the receiver film R after recording.
Step 1: The receiver film R is wound onto the rotating drum 2 (FIG. 11a).
Step 2: To form K image, a K transfer film is wound onto the receiver film (FIG. 11b).
Step 3: If necessary, the K transfer film is laminated to the receiver film under a partly shown rotating roller (FIG. 11c).
Step 4: Using K image and character data, laser beam is applied to record image (FIG. 11d).
Step 5: The K transfer film is stripped from the image receiving sheet to complete the process of K image recording (FIG. 11e).
Step 6: The same procedure is repeated to record C image.
The C transfer film is wound onto the image receiving sheet.
Step 7: The C transfer film is laminated to the image receiving sheet as needed.
Step 8: Perform laser recording with C data.
Step 9: Strip the C transfer film from the image receiving sheet to complete the process of C image recording.
Step 10: The same procedure is repeated to record M image.
The M transfer film is wound onto the image receiving sheet.
Step 11: The M transfer film is laminated to the image receiving sheet as needed.
Step 12: Perform laser recording with M data.
Step 13: Strip the M transfer film from the image receiving sheet to complete the process of M image recording.
Step 14: The same procedure is repeated to record Y image.
The Y transfer film is wound onto the image receiving sheet.
Step 15: The Y transfer film is laminated to the image receiving sheet as needed.
Step 16: Perform laser recording with Y data.
Step 17: Strip the Y transfer film from the image receiving sheet to complete the process of Y image recording.
Step 18: By these steps, the desired color image is formed, with K, C, M and Y colors superposed as appropriate on the receiver film (FIG. 11f).
Thus, in the recording apparatus, the recording medium consisting of the receiver film intimately overlaid with the transfer film using a heat fusible toner, a heat bonding toner or a sublimable toner is fixed on the rotating drum and illuminated with a laser beam from the optical head to record K, C, M and Y images either individually or in superposition.
The conventional recording mediums have had the problem that the toner layer in the transfer film deforms during recording to eventually cause a drop in density. This can be ascribed to the following two facts. First, in the conventional recording medium, a peak temperature observable in the direction of thickness occurs in the central portion of the opto-thermal converting layer. Second, the solvent used in the step of coating the support with the opto-thermal converting layer cannot be entirely removed in the subsequent drying step but partly remains in the dried opto-thermal converting layer. Since the central part of the opto-thermal converting layer becomes hot upon exposure to laser beam, the residual solvent in that central part evaporates to form gas; what is more, the opto-thermal converting layer has such a dense structure that the evaporating gas cannot dissipate to the outside but stays within to bulge the opto-thermal converting layer and eventually deform the toner layer.
The present invention has been accomplished under these circumstances and has as an object providing a recording medium in which the thickness of an opto-thermal converting layer can be adjusted to have general agreement with the position of a peak in temperature profile across the thickness of the opto-thermal converting layer.
This object of the invention can be attained by the recording apparatus recited in claim 1, which superposes a transfer film on an receiver film, said transfer film having an opto-thermal converting layer and a toner layer on a support and said receiver film having an image receiving layer on a support, said toner layer being opposed to said image forming layer, transfers said toner layer onto said image receiving layer by exposure of laser beam, and strips said transfer film from said receiver film to form an image, characterized in that the thickness of said opto-thermal converting layer is adjusted such that the distance from the position where a peak temperature occurs in the direction of thickness of the opto-thermal converting layer to said toner layer is within the range from zero to a third of the thickness of said opto-thermal converting layer.
The stated object of the invention can also be attained by the recording method recited in claim 2, which comprises the steps of superposing a transfer film on an receiver film, said transfer film having an opto-thermal converting layer and a toner layer on a support and said receiver film having an image receiving layer on a support, said toner layer being opposed to said image forming layer, transferring said toner layer onto said image receiving layer by exposure of laser beam, and stripping said transfer film from said receiver film to form an image, characterized in that the thickness of said opto-thermal converting layer is adjusted such that the distance from the position where a peak temperature occurs in the direction of thickness of the opto-thermal converting layer to said toner layer is within the range from zero to a third of the thickness of said opto-thermal converting layer.
The stated object of the invention can also be attained by the transfer film recited in claim 3 which has an opto-thermal converting layer and a toner layer on a support and which is characterized in that said opto-thermal converting layer has a thickness of 0.1-0.3 xcexcm.
By adopting the structural designs described above, the thickness of the opto-thermal converting layer can be adjusted to have general agreement with the position of a peak in temperature profile across the thickness of the opto-thermal converting layer. Even if a gas evolves in the opto-thermal converting layer during exposure to laser beam, it can easily dissipate to the outside of the recording medium and will not remain in the opto-thermal converting layer; as a result, there is no bulging of the opto-thermal converting layer and satisfactory recording can be accomplished.
The stated object of the invention can also be attained by the recording apparatus recited in claim 4, which superposes a transfer film on an receiver film, said transfer film having an opto-thermal converting layer and a toner layer on a support and said receiver film having an image receiving layer on a support, said toner layer being opposed to said image forming layer, transfers said toner layer onto said image receiving layer by exposure of laser beam, and strips said transfer film from said receiver film to form an image, characterized in that at least one parameter selected from among the diameters, powers, arrangement, number and wavelengths of recording spots of said laser beam is adjusted such that the distance from the position where a peak temperature occurs in the direction of thickness of the opto-thermal converting layer to said toner layer is within the range from zero to a third of the thickness of said opto-thermal converting layer.
This design permits the intended adjustment of the distance of interest by appropriate adjustment of laser beam. Even if a gas evolves in the opto-thermal converting layer during exposure to laser beam, it can easily dissipate to the outside of the recording medium and will not remain in the opto-thermal converting layer; as a result, there is no bulging of the opto-thermal converting layer and satisfactory recording can be accomplished.